“Even if scientists could engineer single-nutrient foods and measure and track diet with precision, the research would still be complicated by the fact that food is just one of many factors that impact health. “The biggest problem in nutrition science is that we can’t reduce whatever effect we’re looking at to one component,” says Linda Bacon, researcher and author of Health at Every Size. “Exercise, relationships, sleep, stress, and a long list of other things will affect health beyond nutrition. And yet when you’re doing a study on nutrients, all you’re looking at is nutrition.” Maybe someone is eating eggs for breakfast every day but also has a stressful job and never gets more than six hours of sleep. If this person has heart-health issues down the line, it’s impossible to say that eggs are the culprit.
Researchers do often take into account factors like race, socioeconomic status, and gender. It’s widely accepted that these things can be stronger determinants of health than diet, Bacon says. But other influencing factors are nearly impossible to control for, like chronic mental-health problems, food anxiety, and genetics.”